fix

tests/test_sweep_reader.py

@@ -44,6 +44,28 @@ def _pack_log16_point(step: int, real: int, imag: int) -> bytes:
     )
 
 
+def _pack_tty_start() -> bytes:
+    return b"".join(
+        [
+            _u16le(0x000A),
+            _u16le(0xFFFF),
+            _u16le(0xFFFF),
+            _u16le(0xFFFF),
+        ]
+    )
+
+
+def _pack_tty_point(step: int, ch1: int, ch2: int) -> bytes:
+    return b"".join(
+        [
+            _u16le(0x000A),
+            _u16le(step),
+            _u16le(ch1),
+            _u16le(ch2),
+        ]
+    )
+
+
 def _chunk_bytes(data: bytes, size: int = 4096) -> list[bytes]:
     return [data[idx : idx + size] for idx in range(0, len(data), size)]
 
@@ -111,6 +133,28 @@ class SweepReaderTests(unittest.TestCase):
             reader.join(timeout=1.0)
             stack.close()
 
+    def test_parser_16_bit_x2_falls_back_to_tty_ch1_ch2_stream(self):
+        payload = bytearray()
+        while len(payload) < (_PARSER_16_BIT_X2_PROBE_BYTES + 24):
+            payload += _pack_tty_start()
+            payload += _pack_tty_point(1, 100, 90)
+            payload += _pack_tty_point(2, 120, 95)
+            payload += _pack_tty_point(1, 80, 70)
+
+        stack, reader, queue, stop_event, stderr = self._start_reader(bytes(payload), parser_16_bit_x2=True)
+        try:
+            sweep, info, aux = queue.get(timeout=2.0)
+            self.assertEqual(info["ch"], 0)
+            self.assertIsNotNone(aux)
+            self.assertGreaterEqual(sweep.shape[0], 3)
+            self.assertAlmostEqual(float(sweep[1]), 10.0, places=6)
+            self.assertAlmostEqual(float(sweep[2]), 25.0, places=6)
+            self.assertIn("fallback -> legacy", stderr.getvalue())
+        finally:
+            stop_event.set()
+            reader.join(timeout=1.0)
+            stack.close()
+
     def test_parser_16_bit_x2_keeps_true_complex_stream(self):
         payload = b"".join(
             [